1. Field of The Invention
The present invention is related to tractor trailers and, more particularly, is directed towards an improvement in tractor trailers intended to facilitate the coupling therebetween.
2. Description of The Prior Art
Tractor trailers which incorporate fifth wheel coupling mechanisms are well-known in the trucking industry. The term "fifth wheel" generally refers to a coupling mechanism positioned in the rear frame assembly of a tractor. A typical fifth wheel assembly includes a swivel plate pivotally mounted to the frame assembly and comprises a substantially planar plate having a pair of rearwardly depending ram members which define a V-shaped receiving slot for the kingpin of the trailer.
The kingpin depends downwardly from a steel plate or apron formed on the underside of the trailer frame at the forward end thereof. The normal manner of coupling the tractor to the trailer is to back the tractor up until the forward end of the apron engages the ramps on the fifth wheel assembly at which point the apron is guided up, the kingpin is automatically centered via the V-shaped slot, and the plate pivots to accept the kingpin at the center thereof. A locking mechanism is normally positioned below the swivel plate of the fifth wheel assembly to lock the kingpin in place when properly seated. The kingpin permits the trailer to swivel on the fifth wheel while the vehicle is turning either in a forward or reverse direction.
One problem arises when the trailer vehicle is for some reason positioned lower than the optimum height for coupling with the tractor. This can occur, for example, as a result of an overloaded trailer, uneven or soft ground, or the like. When the trailer, and hence apron and kingpin, are not in the proper horizontal plane, backing up of the tractor can cause severe damage to the front of the trailer, the rear of the tractor, the fifth wheel assembly, the kingpin and apron, and other parts of the coupling assembly. In other words, if the dolly wheels or pads of the trailer have settled into the ground, backing up of the tractor may, for example, create an impact between the rearwardly extending frame members of the tractor and the boxcar of the trailer to cause damage to either or both. This leads, in turn, to costly repairs and down times.
Prior United States patents in this general art area of which I am aware include: 1,084,820; 1,548,967; 1,623,990; 1,785,697; 1,951,258; 2,480,483; and 3,811,706. However, none of the foregoing address the problem referred to above.